Cheat Sheet Network Proprofs

Networking Facts A network is network  is a group of computers (often called nodes or  hosts) hosts) that can share information information through through their interconnect interconnections. ions. A network network is made up of the following components: •

Computer systems (nodes or hosts)

•

Transmission media--a path for electrical signals between devices

•

Network Network interfaces interfaces--dev --devices ices that send and receive receive electrical electrical signals

•

Prot Protoc ocol olss--r -rul ules es or stan standa dard rds s communicate and exchange data

that that

desc describ ribe e

how how

host hosts s

There are several ways to classify networks. The following table lists several ways to describe a network. Network Network Type Type Descripti Description on Host Role In a peer to peer network, the hosts provide and consume network services, and each host has the same operating system. Advantages of peer to peer networks include:

Peer-to-Peer 

•

Easy implementation

•

Inexpensive

Disadvantages of peer to peer networks include: •

Difficult to expand (not scalable)

•

Difficult to support

•

Lack centralized control

•

No centralized storage

In a client/server network, hosts have specific roles. For  example, some hosts are assigned server roles which allows them to provide network resources to other hosts. Other hosts are assigned client roles which allows them to consume network resources. Unlike peer to peer  networks, hosts in a client/server network have different operating systems.

Baseband

Baseband signaling allows one signal at a time on the network medium (cabling).

Broadband

Broadband signaling divides the network medium into multiple channels, allowing several signals to traverse the medium at the same time.

Networking Configuration Network architecture is a set of standa standards rds for how compute computers rs are physically connected and how signals are passed between hosts. Some typical network architectures are described in the table below. Network Architecture

Description

Ethernet

Ethernet is a wired networking standard and is the most common networking architecture used in LANs.

Dial-up Modem

Dial-up networking is a common way to connect a computer to a remote network, such as the Internet. A modem on each computer uses the phone lines to send and receive data.

DSL is a fast-growing alternative to dial-up networking DSL (Digital to connect to the Internet. DSL uses regular phone Subscriber Line) lines to send digital broadband signals.

Asymmetrical DSL (ADSL)

ADSL offers differing upload and download speeds and can be configured to deliver up to six megabits of data per second (6000K) from the network. network. ADSL enables voice and high-speed data to be sent simultaneously over the existing telephone line.

Rate Adaptive DSL (RADSL)

A non-standard version of ADSL. Note that standard ADSL also permits the ADSL modem to adapt speeds of data transfer.

Very High Bit Rate DSL (VDSL)

Up to 26 Mb/s, over distances up to 50 Meters on short loops such as from fiber to the curb. In most cases, VDSL lines will be served from neighbourhood cabinets that link to a Central Office via optical fiber. VDSL is currently being introduced in market trials to deliver  video services over existing phone lines. VDSL can also be configured in symmetric mode.

High Data Rate DSL (HDSL)

This variety created in the late 1980s delivers symmetric service at speeds up to 2.3 Mbps in both directions. Available at 1.5 or 2 .3 Mbps, this symmetric fixed rate application does not provide standard telephone service over the same line and is already standardized through ETSI and ITU (International Telecommunications Union). Seen as an economical replacement for T1 or E1, it uses one, two or three twisted copper pairs.

Integrated Services Digital Network DSL (IDSL)

This is a form of DSL that supports symmetric data rates of up to 144 Kbps using existing phone lines. It is unique in that it has the ability to deliver services through a DLC (Digital Loop Carrier: a remote device often placed in newer n eighborhoods to simplify the distribution of cable and wiring from the phone company).

Advantages of client/server networks include: Client/Server 

•

Easily expanded

•

Easy to support

•

Centralized services

•

Easy to backup

Disadvantages of client/server networks include: •

Server operating systems are expensive

•

Requires extensive advanced planning

Geography and Size LANs reside in a small geographic area, like in an office. Local Area A series of connected LANs, or a LAN connected across Network (LAN) several buildings or offices, is called an internetwork . Wide Area Network (WAN)

A WAN is a group of LANs that are geographically isolated but connected to form a large internetwork.

Participation

Private

A LAN or WAN for private individual or group use which may or may not be secure. Examples include home and organization networks. Intranets and extranets, extranets, although related to the Internet, are private networks. Both an extranet and intranet are tightly controlled, and made available only to select organizations. An extranet is made available to the public and an intranet is made available internally.

Public

A large collection of unrelated computers, with each node on the network having a unique address. The Internet, for example, is a public n etwork.

ISDN is another alternative to traditional dial-up that can be used to connect to the Internet or to directly communicate with another computer connected to the ISDN network. ISDN can use regular telephone wiring, ISDN (Integrated but must be connected to a special ISDN network. Services Digital • BRI ISDN is 2 “B” Channels at 64Kbps for a total Network) of 124Kbps (BRI=Basic Rate Interface) •

Wireless

PRI ISDN also known as T1 is 23”B” Channels and one 64Kpbs “D” Channel (PRI=Primary Rate Interface)

Wireless networking uses radio waves or i nfrared light to send data between hosts. Most wireless networks connect into larger wired networks which are in turn connected to the Internet.

Signaling

Network+ N10-003 Cheat Sheet

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You do not need to know what each each type of DLS is or does. You may be asked to select what are valid DSL types from a list.

Note:

A mesh topology exists when there are multiple paths between any two nodes on a network. Mesh topologies are created using point-to-point connections. This increases the network's fault tolerance because alternate paths can be used when one path fails. Two variations of mesh topologies exist:

Communication between hosts on a network generally takes one of  three forms: •

Simplex--one-way communication communication from a sender to a receiver.

•

Half-d Half-dupl uplexex--t -twowo-way way commun communica icatio tion n betwee between n two Communication only travels in one direction at a time.

•

hosts hosts..

Duplex--two-way communication between hosts. Communication can travel in both directions simultaneously.

•

Mesh

Topology Facts Topology is Topology is the term used to describe how devices are connected and how messages flow from device to device. There are two types of  network topologies: •

The physical topology describes the physical way the network is wired.

•

The logical topology describes the way in which messages are sent.

The following table describes several common physical topologies. Topolo Topology gy Descri Descripti ption on A physical bus topology consists of a trunk cable with nodes either inserted directly into the trunk, or nodes tapping into the trunk using offshoot cables called drop cables.

Bus

•

Signals travel from one node to all other nodes on the bus.

•

A device called a terminator is terminator is placed at both ends of  the trunk cable.

Terminators absorb signals and prevent them from reflecting repeatedly back and forth on the cable. The physical bus: •

•

Requires less cable than the star 

•

Can be difficult to isolate cabling problems

•

A ring topology connects neighboring nodes until they form a ring. Signals travel in one direction around the ring. In ring topologies, each device on the network acts as a repeater to send the signal to the next device. With a ring:

•

Instal Installat lation ion requir requires es carefu carefull planni planning ng to creat create e a continuous ring.

•

Isolating problems can require going to several physical locations along the ring.

•

A malfu malfunct nction ioning ing node node or cable cable break break can preven preventt signals from reaching nodes further along on the ring.

•

MSAU’ MSAU’s s use “RING “RING IN” and “RING “RING OUT” OUT” ports ports for  multiple multiple MSAU’s. MSAU’s. These need need to be configured configured in the proper order. With multiple MSUA’s MSUA’s the “ring out” needs to connect to the “ring in” in order to complete the ring.

•

Adding a work station to a physical ring topology will disconnect all clients from the network.

•

Token Token Ring Ring 802.5: 802.5: Rememb Remember er that that Token Token Ring Ring networks do not have any collisions as they use a token pass to to communicate. communicate. Questions regarding networks networks where where no collisions collisions are the highest highest priority could be referring referring to Token Token Ring. A Token Ring network network also provides equal access to all computers.

Ring

A star star topolo topology gy uses uses a hub (or switc switch) h) to concen concentra trate te all network connections to a single physical location. With the star: •

All network connections are located in a single place, which makes it easy to troubleshoot and reconfigure.

•

Nodes can be added to or removed from the network easily.

•

Cabling problems usually affect only one node.

•

Requires Requires more cable than any other topology. topology. Every node has its own cable.

Star 

Network+ N10-003 Cheat Sheet

Partial Mesh--Some redundant paths exist.

Full Mesh--Every node has a p oint-to-point connection with every other node. Full mesh topologies are u sually impractical because the number of connections increases dramatically with every new node added to the network. However, a full mesh topology becomes more practical through the implementation of an adhoc wireless network. With this topology, every wireless network card can communicate directly with any other  wireless network card on the network. A separate and dedicated network interface and cable for each host on the network is not required. •

Logical Topologies A logical topology is the way that the signals act on the network media, or the way that the data passes through the network from one device to the the next next withou withoutt regard regard to the the physic physical al interc interconn onnect ection ion of the devices. Logical topologies are bound to the network protocols that direct how the data moves across a network. In the Bus Logical Topology each time a node on the network has data for another node; the sending node broadcasts the data to the entire network. The various nodes hear hear it and look to to see if the data data is for  them. If so, they keep the data. data. If not they ignore ignore the data. data. Ethernet is the best known example example of a logical bus network. LocalTalk is also another example of a logical bus network. In the Ring Logical Topology Topology only one node can send informat information ion across the network at any given time. This is achieved by way of a token. token. The Token Ring and Fiber Distribut Distributed ed Data Interface Interface are examples of a Logical Ring Network Note: Remember if you see logical  in the question about a 10BaseT, 100BaseT network it is referring to the bus topology. To connect to a TCP/IP network you do not need a default Gateway, unless you are required to connect to the Internet or another network, to be entered into the client configuration. configuration. Only an IP address and a subnet mask are required to be able to communicate on the network. A default gateway is required for access to another network such as the internet. 100VG-anyLAN IEEE 802.12 also called Demand Priority. The VG stands for Voice Grade the 100 is obviously 100Mbps while the “anylan” part refers to the ability to work within just about any Ethernet Ethernet LAN technology. technology. Questions about this topic may include what method access is used by 100VG 100VG-an -anyLA yLAN. N. The differ differenc ence e here is Demand Demand Priority  Priority  over  CMSA/CD that is part of 802.3 Ethernet protocol. Twisted Pair Facts Twisted pair cables support a wide variety of fast, modern network stan standa dard rds. s. Twis Twiste ted d pair pair cabli cabling ng is comp compos osed ed of the the foll follow owin ing g components: •

Two wires that carry the data signals (one conductor carries a positive signal; one carries a negative signal). They are made of  22 or 24 gauge copper wiring.

•

PVC or plenum plastic insulation surrounds each wire. Plenum cable is fire resistant and non-toxic. It must be used when wiring above above ceiling ceiling tiles. PVC cable cannot be used to wire above ceilings because it is toxic when burned.

•

Two wires are twisted to reduce the effects of  electromagnetic  interference (EMI) and crosstalk . Because the wires are twisted, EMI should affect both wires equally and can be cancelled out.

•

Multi Multiple ple wire wire pairs pairs are bundle bundled d toget together her in an outer outer sheath sheath.. Twisted pair cable can be classified according to the makeup of  the outer sheath:

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o

o

Shielded Twisted Pair (STP) has a grounded outer copper  shield around the bundle of twisted pairs or around each pair. This provides added protection against EMI. Unshielded Twisted Pair (UTP) does not have a grounded outer copper shield. UTP cables are easier to work with and are less expensive than shielded cables.

The table below describes the different unshielded twisted pair (UTP) cable types (categories). Type

Connec to tor Descrip ti tion

Phone cable

RJ-1 RJ-11 1

Cat 3

RJ-45

Designe d for us use wi with 10 10 me megabi t Ethe rn rnet or or 16 16 megabit token ring.

Cat 5

RJ-45 -45

Suppor pportts 100 100 mega egabit bit and 1 giga gigabi bitt Ether hernet net and and ATM networking.

Cat Cat 5e 5e

RJ-4 RJ-45 5

Simi Simila larr to to Cat Cat 5 but but prov provid ides es bett better er EMI EMI prot protec ecti tion on.. Supports 1 and 10 gigabit Ethernet (gigabit connections require the use of all four twisted pairs).

Used Used to conn connec ectt a PC to a pho phone ne jack jack in a wal walll outlet to establish a dial-up Internet connection. Has two pairs of twisted cable (a total of 4 wires).

Cat 6

RJ-45

Supports hi high-bandwidth, br broadband communications.

Cat-6 STP

RJ-4 RJ-45 5

Used Used for for dat data tran transm smis issi sion ons. s. Supp Suppor orts ts up to to 600 600 MHz and used in Ethernet, Fast Ethernet, Gigabit Ethernet, Token Ring, and 155 Mbps ATM.

The easiest way to create a crossover  crossover  cable is to arrange the wires in the first connector connector using the T568A standard standard and arrange arrange the wires in the second second connector using the T568B standard.

Ethernet specifications use the following pins (Tx is a pin used for  transmitting and Rx is a pin used for receiving): •

Pin 1: Tx+

•

Pin 2: Tx-

•

Pin 3: Rx+

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Pin 4: Unused

•

Pin 5: Unused

•

Pin 6: Rx-

•

Pin 7: Unused

•

Pin 8: Unused

Coaxial Cable Facts Coaxial cable is an older technology that is usually implemented with a bus topology. It is not suitable for ring or star topologies because the ends ends of the the cabl cable e must must be term termin inat ated ed.. It is comp compos osed ed of two two conductors, which share a common axis, within a single cable. Coaxial cable is built with the following components: •

Two concentric metallic conductors: The inner conductor conductor,, which carries carries data signals. It is o made of copper or copper coated with tin. The mesh conductor is a second physical channel that o also grounds the cable. It is made of aluminum or copper  coated tin.

•

The insulator, which surrounds the inner conductor, keeps the signal separated from the mesh conductor. It is made of PVC plastic.

•

The mesh conductor, which surrounds the insulator and grounds the cable. It is made of aluminum or copper coated tin.

•

The PVC sheath, which is the cable encasement. It surrounds and protects the wire. It is made of PVC plastic.

The table below describes describes the two types of connector connectors s used with twisted pair cables. Conne onnect ctor or RJ-11

RJ-45

Des Descri criptio ption n •

Has 4 connectors

•

Supports up to 2 pairs of wires

•

Uses Uses a lockin locking g tab to keep keep connec connector tor secure secure in outlet

•

Used primarily for telephone wiring

•

Has 8 connectors

•

Supports up to 4 pairs of wires

•

Uses Uses a lockin locking g tab to keep keep connec connector tor secure secure in outlet

•

Used for Ethernet and some token ring connections

Each type of UTP cable can be substituted for any category below it, but never for a category above. For example, Cat 6 can be substituted for a task requiring Cat 5e; however, neither Cat 5 nor Cat 3 should be used for this particular task. Making Cable Facts Twisted pair cables remain one of the primary ways that computers connect to a network. Computers connect to the network through a hub or switch with a straight-through cable. Computers can connect directly to one another using a crossover cable.

Coaxial cable has the following advantages and disadvantages: Advantages

Disadvantages

Description

Grade

•

Network+ N10-003 Cheat Sheet

T568 T568AA--T -To o use use this this stan standa dard rd,, arrange the wires from pins 1 to 8 in each connector in the following orde order: r: GW, GW, G, OW, B, BW, O, BrW, Br. T568 T568BB--T -To o use use this this stan standa dard rd,, arrange the wires from pins 1 to 8 in each connector in the following orde order: r: OW, OW, O, GW, B, BW, G, BrW, Br.

•

Highly resistant to physical damage

•

Expensive

•

Inflexible construction (difficult to install)

•

Unsupported by newer networking standards

Uses •

RG-58

There are two standards for creating creating straight-through cables: •

Highly resistant to EMI (electromagnetic interference)

The table below describes the different coaxial cable grades.

The table below illustrates both straight-through and crossover cable configurations. Cable

•

•

10Base2 Ethernet networking (also known as Thinnet)

Resistance Rating

50 ohms

Limited to 185 meters

RG-59

Cable TV and cable networking

75 ohms

RG-6

Satellite TV

75 ohms

•

RG-8 •

10Base5 Ethernet networking (also known as Thicknet)

50 ohms

Limited to 500 meters

Page 3

The table below describes the types of connectors used with coaxial cable. Connector

Description

F-Type

BNC

•

Twisted onto the cable

•

Used to create cable and satellite TV connections

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Used to hook a cable modem to a broadband cable connection

•

Also referred to as ‘T Connectors’

•

Molded onto the cable

•

Used in 10Base2 Ethernet networks

•

DB15 serial connector 

•

Used in 10Base5 Ethernet networks

AUI

Fiber Optic Facts To connect computers using fiber optic cables, you need two fiber  strands. One strand transmits signals, and the other strand receives signals. Fiber optic cabling is composed of the following components: •

The core carries the signal. It is made of plastic or glass.

•

The cladding maintains the signal in the center of the core as the cable bends.

•

The sheathing protects the cladding and the core.

Subscriber Connector (SC)

Fiber optic cabling offers the following advantages and disadvantages: Advantages

Disadvantages

•

Totally immune to EMI (electromagnetic interference)

•

Highly resistant to eavesdropping

•

Supports extremely high data transmission rates

•

Allows greater cable distances without a repeater 

•

Very expensive

•

Difficult to work with

•

Special training required to attach connectors to cables

•

Also called a push in and twist connector 

•

Each wire has a separate connector 

•

Nickel plated with a ceramic ferrule to insure proper core alignment and prevent light ray deflection

•

As part of the assembly process, it is necessary to polish the exposed fiber tip to ensure that light is passed on from one cable to the next with no dispersion

•

Used with single- and multi-mode cabling

•

Push on, pull off connector type that uses a locking tab to maintain connection

•

Each wire has a separate connector 

•

Uses a ceramic ferrule to insure proper core alignment and prevent light ray deflection

•

As part of the assembly process, it is necessary to polish the exposed fiber tip

•

Used with single- and multi-mode cabling

•

Composed of a plastic connector  with a locking tab, similar to a RJ-45 connector 

•

A single connector with two ends keeps the two cables in place

•

Uses a ceramic ferrule to insure proper core alignment and prevent light ray deflection

•

Half the size of other fiber-optic connectors

Lucent Connector (LC)

Multi-mode and single mode fiber cables are distinct from each other  and not interchangeable.

•

Used with single and multimode cabling

•

Composed of a plastic connector with a locking tab

•

Uses metal guide pins to ensure it is properly aligned

The table below describes multi-mode and single mode fiber cables. Type

Single Mode

Multimode

Mechanical Transfer-Registered Jack Connector (MT-RJ)

Description •

Transfers data through the core using a single light ray (the ray is also called a mode)

•

•

The core diameter is 8 to 10 microns and 125 micron cladding

A single connector with one end holds both cables

•

•

Supports a large amount of data

•

Cable lengths can extend a great distance

Uses a ceramic ferrule to insure proper core alignment and prevent light ray deflection

•

Full duplex

•

Connectors are: MT-RJ and LC

•

Transfers data through the core using multiple light rays

•

The core diameter is 50 to 100 microns and 125 micron cladding

•

Cable lengths are limited in distance (550 meters)

•

Full duplex

Fiber optic cabling uses the following connector types: Type Straight Tip (ST) Connector 

Description •

•

Network+ N10-003 Cheat Sheet

Used with single and multi-mode cabling Keyed, bayonet-type connector 

802.3z The Gigabit Ethernet SX feature is a TCP/IP attachment that offers high-speed data transfers using multi-mode optical fiber . 1000BASESX USB and FireWire Facts You can create a network connection between two PCs by plugging a USB cable into their USB ports. You can also use software that allows you to connect multiple PCs through a USB hub. USB is a serial communication specification. There are two USB versions: •

USB 1.0 runs at 12 megabits per second.

•

USB 2.0 runs at 480 megabits per second.

The table below describes the three types of USB connectors. Connector

Description

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A Connector 

•

Generally plugs directly into the computer or a hub

•

To connect two computers together  directly, select a USB cable with two A connectors

•

Generally plugs into a hub, printer, or  other peripheral device to connect the device to the computer 

•

Most USB cables have an A connector  on one end (to connect to the cable) and a B connector on the other end (to connect to the device)

B Connector 

•

Designed to plug in to devices with mini plugs such as a digital camera

•

Most USB cables with a mini connector have an A connector on the other end to connect to the computer 

Mini Connector 

You can also create a network connection between two PCs using their FireWire (IEEE 1394) ports. The table below describes Firewire and its connectors. Connector

in the original assignment can apply for a new MAC address assignment. A NIC communicates across the network using the following method: 1. The NIC receives data from the PC. 2. The NIC breaks the data into frames, which include the following information: o The receiving NIC's MAC address o The sending NIC's MAC address The data it is transmitting The CRC (cyclic redundancy checking) which is used to verify correct transmission and reception of the data The NIC encodes the frames as electrical or light impulses and transmits them across the network. The receiving NIC verifies the NIC addresses and CRC. The receiving NIC tracks the frames and reassembles the data. The receiving NIC sends the data to the PC. o o

3. 4. 5. 6.

Network Connection Device Facts The following table lists several common connection devices used within a LAN. Device

A hub is the central connecting point of a physical star, logical bus topology. Hubs manage communication among hosts using the following method:

Description

6-pin Connector 

•

Supports data transfer speeds at upwards of 400 Mbps

•

6-pin connector is used when making connections between PCs

•

4-pin connector is used to connect to peripheral devices

4-pin Connector 

Hub

Component Description These connect the network interface and host to the network media.

This visually indicates the network connection status. Link indicator  Green generally indicates a good connection, and red or  an unlit diode indicates a bad connection.

Switch

MAC Address The MAC address is a unique hexadecimal identifier  burned into the ROM (physically assigned address) of  every network interface. •

The MAC address is a 12-digit hexadecimal number  (each number ranges from 0-9 or A-F).

•

The address is often written as 00-B0-D0-06-BC-AC or 00B0.D006.BCAC, although dashes, periods, and colons can be used to divide the MAC address parts.

•

The MAC address is guaranteed unique through design. The first half (first 6 digits) of the MAC address is assigned to each manufacturer. The manufacturer determines the rest of the address, assigning a unique value which identifies the host address. A manufacturer that uses all the addresses

Network+ N10-003 Cheat Sheet

A host sends a frame to another host through the hub.

•

The hub duplicates the frame and sends it to every host connected to the hub.

•

The host to which the frame is addressed accepts the frame. Every other host ignores the frame.

Switches provide functionality similar to hubs, but typically on a larger scale and with higher performance (A switch offers guaranteed bandwidth to each port). Unlike a hub, a switch forwards frames only to the intended host, not every host connected to the switch. A switch builds a database based on MAC addresses to make forwarding decisions.

The table below describes the components of an Ethernet NIC.

A NIC's transceiver is responsible for transmitting and receiving network communications. To send signals to the network, it converts digital data from a PC to digital signals. The type of signal the transceiver sends depends Transceiver  on the type of network. A fiber optic NIC sends light signals; an Ethernet NIC sends electronic signals. To receive signals, the transceiver converts digital signals from the network to digital data for the PC.

•

Active VS’s Passive hubs – Active hubs regenerate the signals while passive hubs do not. Active hubs are generally more expensive than passive hubs. Both passive and active hubs work at the physical layer (layer1) of the OSI model. Use crossover cables and not patch cables to connect multiple hubs together.

Network Adapter Facts A network adapter connects a host to the network medium. Some computers, like laptops, come with built-in network adapters. Other  computers use NICs (network interface cards) that plug in to the system's expansion slots or which are external to the computer and connect through an existing computer port. A common network interface card is one used on an Ethernet network.

Media connectors

Description

•

The process begins by examining the source address of  an incoming packet. If the source address is not in the forwarding database, an entry for the address is made in the database. The port it came in on is also recorded.

•

The destination address is then examined. If the destination address is not in the database, o the packet is sent out all ports except for the one on which it was received. If the destination address is in the database, the o packet is forwarded to the appropriate port if the port is different than the one on which it was received. o Broadcast packets are forwarded to all ports except the one on which they were received.

Eventually, a switch learns the location of all devices on the network. Incoming frames are then sent directly to the switch port to which a specific host is connected. Bridge

Bridges connect separate media segments (networks) that use the same protocol. Like a switch, bridges use MAC addresses to determine a frame's destination and to build a table of device addresses and their corresponding segments. This also allows a bridge to prevent messages within a media segment from crossing over to another segment. This keeps the network from wasting bandwidth by eliminating unnecessary traffic between segments. If a bridge does not

Page 5

have the destination address in its forwarding table, then it will forward it to all ports except the originating port. A transparent bridge can be used to segment a network. It’s called transparent because other devices on the network do not need to be aware of it. This would be used to relieve congestion on a network by segmenting it.

The following table is a quick reference guide to network devices. Device

A wireless access point (WAP) is a hub for a wireless network. A WAP works like a hub except that hosts connect using radio waves instead of wires. Note: A WAP can have ports that interface with a wired portion of a segment, allowing you to connect the WAP to the wired network. Some WAPs even have built-in wired hubs or switches.

Internetwork Device Facts In a broad sense, the term network  can describe any collection of  devices connected together to share information and resources. For  example, the Internet is a worldwide network linking computers so they can share resources. The telephone company is another type of  network, connecting phones and providing services. Likewise, the term internetwork might mean connecting two separately managed networks together, or it might mean connecting two network segments together. Devices such as hubs, switches, and bridges connect multiple devices to the same network segment. Internetwork devices connect multiple networks or subnets together, and enable communication between hosts on different types of networks.

Hub

Switch

Connects all nodes/segments in a network together; filters and forwards packets; isolate collision domains

Layer 2

multiport bridge, configure VLANs

Bridge

Connects 2 network segments with dissimilar  media types; isolate collision domains within a segment

Layer 2

wired or  wireless

Router 

Connects 2 networks with different topologies; maps Layer 3 nodes & routes packets; isolates broadcast domains

Brouter, IOS

Gateway

Connects 2 networks with different protocols or  technologies; could be hardware or software

Layer 4, 5, 6, 7

connection to ISP, PABX

NIC

An expansion card installed in a device to connect/interface to the network; particular to media & protocol

Layer 1, 2

PCI, USB, PCMCIA, builtin M/B

CSU/DSU

A 2 in 1 device used to connect a digital carrier to the network equipment; provides diagnostics & buffering

-

T1, T3; V.35 interface

ISDN adapter 

The terminal adapter used to connect to the internet via ISDN technology

-

BRI TA

WAP

A device used to connect mobile PCs to a wired network wirelessly via RF technology

Layer 1, 2

infrastructure mode, WiFi

Modem

A device that changes digital to analog signal and vice versa; modulator/demodulator 

-

POTS (V.92), xDSL, cable

-

media converter, DIX/AUI

-

port blocking, packet filtering, proxy server, DMZ

Description

A gateway is a generic term used to describe any device that connects one administratively managed network with another. For example, a gateway connects a business network to the Internet. The gateway device controls the flow of data between the two networks. In addition, the term gateway is often used Gateway to describe a specialized device that translates data sent between two networks using different protocols. Gateways work on the top 3 layers of the OSI and are required input within the TCP/IP setting for a client for connection to another  network such as the Internet. A router is a device that connects two or more network segments or subnets.

Router 

•

Each subnet has a unique, logical network address.

•

Routers can be used to connect networks within a single LAN, or they can be used as gateways to connect multiple LANs together.

•

Routers can be used to connect networks with different architectures (such as connect an Ethernet network to a token ring network).

In addition to simply linking multiple subnets together, routers keep track of other subnets on the internetwork and decide the direction data should travel to reach the destination. A firewall is a router with additional security features. Firewalls can be programmed with security rules to restrict the flow of  traffic between networks. •

A firewall can control the type of traffic allowed in to a network and the type of traffic allowed out of a network.

•

Rules set up on the firewall determine the types of  permitted and prohibited traffic.

•

A firewall can be either hardware devices or software installed onto operating systems.

Firewall

Note: There are also some switches (called Layer 3 switches) that have built-in router functionality. These switches examine the logical network address (instead of the MAC address) to switch packets between networks.

Network+ N10-003 Cheat Sheet

Remarks concentrator  (passive), repeater  (active), MAU

The following table lists several common internetworking devices. Device

Operation

Connects all nodes in a network together; transmissions received in 1 Layer 1 port are rebroadcast to all ports

Translational bridges are used when you need to translate data from one format to another across segments. Wireless Access Point (WAP)

Purpose

A device that transmits or  receives analog or digital Transceiver  signals; allows a NIC to connect to a different media type

Firewall

A stand-alone device or  software used to protect networks from spyware, hackers, worms, phising, trojans

Ethernet Facts Ethernet is the most popular networking architecture for LANs. It offers high performance at a low cost and is easy to install and manage.

Page 6

The following table describes various details about Ethernet. Characteristic

Description Ethernet uses one or more of the following networking topologies:

Topology

Media Access Method

•

Physical bus, logical bus

•

Physical star, logical bus

•

Physical star, logical star 

Ethernet uses a contention-based media access method called Carrier Sense, Multiple Access/Collision Detection (CSMA/CD). Devices use the following process to send data. 1. Because all devices have equal access (multiple access) to the transmission media, a device with data to send first listens to the transmission medium to determine if it is free (carrier sense). 2. If it is not free, the device waits a random time and listens again to the transmission medium. When it is free, the device transmits its message. 3. If two devices transmit at the same time, a collision occurs. The sending devices detect the collision (collision detection) and send a jam signal to notify all other hosts that a collision has occurred. 4. Both devices wait a random length of time before attempting to resend the original message (called backoff ). Note: When switches are used on an Ethernet network, collisions disappear. Most devices can detect this and will turn off collision detection and use fullduplex communication. Ethernet supports the following cable types: •

Transmission Media

Physical Addresses

The following table compares the characteristics of various Ethernet implementations. Category Standard

•

Fiber optic, most commonly used in high-speed applications such as servers or streaming media.

•

Coaxial for older Ethernet implementations (often called thinnet or thicknet networks).

•

NICs with transceivers

•

Hubs

•

Switches

•

Routers

Ethernet devices are identified using the MAC address which is burned into the network interface card.

10 G Ethernet

Frames

The preamble is a set of alternating ones and zeroes terminated by two ones (i.e., 11) that marks it as a frame.

•

The destination address identifies the receiving host's MAC address.

•

The source address identifies the sending host's MAC address.

•

The data, or the information that needs to be transmitted from one host to the other.

•

Optional bits to pad the frame. Ethernet frames are sized between 64 and 1518 bytes. If the frame is smaller than 64 bytes, the sending NIC places "junk" data in the pad to make it the required 64 bytes.

•

The CRC (cyclical redundancy check) is the result of a mathematical calculation performed on the frame. The CRC helps verify that the frame contents have arrived uncorrupted.

Network+ N10-003 Cheat Sheet

Maximum Segment Length

100 meters

10BaseFL

10 Mbps (multimode cable)

Fiber optic

1,000 to 2,000 meters

100BaseT4

100 Mbps (half duplex) 200 Mbps (full duplex)

Twisted pair  (Cat5 or higher) 100 meters Uses 4 pairs of  wires

100BaseFX

100 Mbps (multimode cable)

Fiber optic

412 meters

1000BaseT

UTP Twisted pair (Cat5e)

100 meters

1000BaseCX (short copper)

25 meters, used Special copper  within wiring (150 ohm), STP closets

1,000 Mbps (half duplex) 1000BaseSX 2,000 Mbps MM fiber –50 (full duplex) Micron (short)

220 to 550 meters depending on cable quality

1000BaseLX (long)

550 (multimode) MM fiber optic or  10 Km (singleSM fiber optic mode)

10 GBaseSR

MM Fiber optic

10 GBaseLR 10 Gbps (full SM Fiber optic duplex only) 10 GBaseER

SM Fiber optic

2 to 300 meters 2 to 10 kilometers 2 to 40 kilometers

You should also know the following facts about Ethernet: •

The maximum cable length for UTP Ethernet "T" implementations is 100 meters for all standards.

•

You may also see 10Base2 and 10Base5 Ethernet implementations, both of which are older implementations using coaxial cable. You will not be required to know these for the Network+ exam.

•

Ethernet standards support a maximum of 1024 hosts.

A frame is a unit of data that is ready to be sent on the network medium. Ethernet frames contain the following components: •

Cable Type

10BaseT

Fast Ethernet

Gigabit Ethernet

Bandwidth

10 Mbps (half  duplex) Twisted pair  20 Mbps (full (Cat3, 4, or 5) duplex)

Ethernet

Unshielded twisted-pair cables (UTP) with RJ-45 connectors. This is the most common transmission medium used for Ethernet.

Devices used on Ethernet networks include: Networking Devices

Ethernet Specifications Ethernet standards are defined by the work of the IEEE 802.3 committee.

Token Ring Facts Token ring began as a proprietary networking standard developed by IBM. Now there is a public token ring networking standard created by the IEEE 802.5 committee and other vendors that manufacture token ring components. Token ring was a popular networking architecture that is quickly being replaced by Ethernet. However, you may still encounter token ring in some existing networks. Token ring networks have the following advantages: •

There are no collisions.

•

The transmitting host can use the entire bandwidth to send its data.

•

You can assign priorities to designated hosts to give them greater  network access.

•

Troubleshooting broken network connections is made easy by built-in diagnostic devices.

Page 7

Token ring networks have the following disadvantages: The following table describes various details about FDDI.

•

Higher cost than Ethernet networks.

•

Slower operating speeds than Ethernet networks.

Characteristic

Description

Topology

FDDI networks are wired using a physical ring, logical ring topology or a physical star, logical ring topology. FDDI uses dual counter-rotating rings for data (two rings are used, with each sending data in the opposite direction).

Media Access Method

FDDI uses a token-passing media access method. FDDI provides a ring wrapping feature which uses both rings for sending data. If a break occurs in one ring, data can be sent on the other ring, thus isolating the break.

Transmission Media

As the name suggests, FDDI networks use fiber optic cables. Newer specifications allow the use of Cat 5 UTP (sometimes called CDDI ).

The following table describes various details about token ring. Characteristic

Description

Topology

Token ring networks are wired using a physical star, logical ring topology (a physical ring topology is also possible but not common).

Media Access Method

Token ring uses a token-passing media access method: 1. A token passes from host to host. 2. When a host needs to transmit, it grabs the token. 3. The host encapsulates its data into a frame and transmits it around the ring. 4. Each host examines the recipient address of the frame until it arrives at the recipient. 5. The recipient transmits a success frame to the transmitting host to confirm that it received the data. 6. Once it receives a success frame, the sending host creates and releases a new token.

FDDI networks use fiber optic connectors. SC and ST are both fiber optic connectors and can be used on an FDDI network though the MIC connector is the most common. Two types of devices might be connected to an FDDI network:

Networking Devices

A host can communicate directly only with machines immediately upstream or downstream from them in the data flow. A broken ring results when a host fails. Other  hosts on the network can no longer communicate with any hosts downstream from the break. Token ring networks support the following transmission media: •

Transmission Media

STP and UTP

•

Fiber optic

Token Ring uses several types of drop cables to connect workstations to the MSAU (multistation access unit): •

•

Networking Devices

Speed

Type 1 or Type 2 shielded twisted pair (STP) wiring with a DB-9 connector. Category 3 (4 Mbps) or Category 5 (16 Mbps) unshielded twisted pair (UTP) cabling with RJ-45 connectors.

The central connecting point for a token ring network is an MAU (multi-station access unit). You can uplink MAUs by connecting patch cables between the RI (ring in) and RO (ring out) ports on each MAU. Be aware that you must connect both sets of RI and RO ports on both MAUs to make sure the ring is complete.

•

LAN Backbones--The FDDI network backbone for the rest of the network.

•

Computer-room Networks--These networks performance mainframes and other computers.

•

High-speed LANs--The speed of FDDI is ideal for networks with high data traffic, powerful workstations (engineering or computeraided design workstations), or networks requiring high transfer  rates (i.e. digital video).

Network+ N10-003 Cheat Sheet

forms

a

high-speed

connect

•

Single Attachment Stations (SAS), also called Class B devices, attach to one ring (primary).

FDDI operates at 100 Mbps on a single ring. When both rings are used, data can travel at an effective rate of 200 Mbps.

Additional Specifications

FDDI can operate over distances up to 200 km (124 miles). When two rings are used, the distance is limited to 100 km (62 miles). FDDI networks can support up to 1000 devices.

Infrared Facts Infrared wireless networking employs light waves that are outside of  the visible light spectrum. It uses light from three regions: •

The near IR band (the light wave closest to the color red)

•

The intermediate (IM) IR band

•

The far IR band

Infrared devices can operate in one of two modes: Method

Description •

Devices must have a direct LoS (line-of-sight) connection and the maximum distance between devices is 1 meter.

•

Because of the LoS connection requirement, communication signals are easily interrupted.

•

Diffuse mode (also called scatter mode) operates by broadcasting a large beam of light rather than a narrow beam. It does not require LOS connections.

•

Despite its advantages, diffuse mode still operates under range limitations. The IR access point and devices must be in the same room with each other.

•

Diffuse mode is also subject to signal disruptions (such as from obstructions).

Line of  Sight (LoS)

Common token ring networks operate at either 4 or 16 Mbps. Newer standards include 100 Mbps and Gigabit (1000 Mbps) token ring, although these have never  been widely adopted.

FDDI Facts Fiber Distributed Data Interface (FDDI) is a fiber-optic, token-ring architecture originally standardized by the American National Standards Institute (ANSI). This standard is in many respects similar to the IEEE 802.5 standard, but is characterized by higher data transfer  rates (100 to 200 Mbps). FDDI is typically implemented in situations where high data transfer  rates are needed, including:

Dual Attachment Stations (DAS), also called Class A devices, attach to both rings (primary and secondary).

Speed

Special IBM-type cables

•

•

Diffuse Mode

You should know the following facts about wireless IR: •

IR data transfers occur at 4 Mbps.

•

IR networks are very insecure because the signals are not encrypted, and they can be easily intercepted.

•

A common use for IR in networking is in transferring data between a handheld or notebook computer and a desktop computer.

high-

Wireless Architecture Facts

Page 8

When you implement a radio frequency wireless network, you use radio waves rather than wires to connect your hosts. Radio waves are considered unbounded media because, unlike wires, they have nothing to encase them. The most commonly used frequency for wireless networking is the 2.4 GHz frequency.

•

Note: Many wireless access points include ports (or  hubs, switches, or routers) to connect the wireless network to the wired portion of the network.

The following table describes details of a wireless networking architecture. Characteristic Description

Signaling Method

Frequency Hopping Spread Spectrum (FHSS)

DirectSequence Spread Spectrum (DSSS)

FHSS uses a narrow frequency band and 'hops' data signals in a predictable sequence from frequency to frequency over a wide band of frequencies. Because FHSS hops between frequencies, it can avoid interference on one cable as it shifts to another. Hopping between frequencies increases transmission security by making eavesdropping and data capture more difficult. Because FHSS shifts automatically between frequencies, it can avoid interference that may be on a single frequency. FHSS applies to 802.11 is still in use with Bluetooth. The transmitter breaks data into pieces and sends the pieces across multiple frequencies in a defined range. DSSS is more susceptible to interference and less secure then FHSS. •

Ad hoc

Works in peer-to-peer mode without a WAP (the wireless NICs in each host communicate directly with one another)

•

Uses a physical mesh topology

•

Cheap and easy to set up but cannot handle more than four  hosts

•

Requires special modifications to reach wired networks

Wireless Standards Radio frequency wireless networking standards are specified by various IEEE 802.11 committees. Wireless networking technologies Standard

Data Speed

Frequency

Transmission Type

Topology

Range

IEEE 802.11 Legacy

2 Mbps

2.4 GHz

FHSS or DSSS

Point-point

30 m

IEEE 802.11b WiFi

11 Mbps

2.4 GHz

DSSS with CCK

Point-point

30 m

IEEE 802.11a WiFi

54 Mbps

5 GHz

OFDM

Point-point

30 m

IEEE 802.11g WiFi

54 Mbps

2.4 GHz

>20 Mbps: OFDM,